1. Technical Field
The present invention relates to a pedestal assembly having a riser shaft extending from a plate. More particularly, the present invention relates to adjusting the riser shaft to change the positional properties of the plate. Specifically, the present invention relates to an alignment assembly disposed between the riser shaft and a drive shaft for use in changing the relative position of the plate of the pedestal assembly within a processing chamber of a reactor such that a more precise alignment, and uniform spacing can be made between the plate and the internal walls of the reactor.
2. Background Information
Semiconductor fabrication processes are typically conducted with the substrates supported within a chamber under controlled conditions. For many purposes, semiconductor substrates (e.g., wafers) are heated inside the process chamber. For example, substrates can be heated by direct physical contact with an internally heated wafer holder or “chuck.” “Susceptors” are wafer supports used in systems where the wafer and susceptors absorb heat from a heater.
Some of the important controlled conditions for processing include, but are not limited to, fluid flow rate into the chamber, temperature of the reaction chamber, temperature of the fluid flowing into the reaction chamber, and wafer position on the susceptor.
Heating within the reaction chamber can occur in a number of ways, including lamp banks or arrays positioned above the substrate surface for directly heating the susceptor or susceptor heaters/pedestal heaters positioned below the susceptor. Traditionally, the pedestal style assembly extends into the chamber through a bottom wall and the susceptor is mounted on a plate of the pedestal assembly. The plate may include a resistive heating mechanism enclosed within the plate to provide conductive heat and increase the susceptor temperature. Alternatively, the system may provide for a heat lamp above the plate to heat the wafer from above within the reaction chamber.
The pedestal style assembly resembles a shaft extending from a disk which encloses the heating mechanism. The susceptor may be connected to the disk and the wafer is placed in or on the susceptor, for example, within a wafer-shaped recessed area defined by the susceptor, or the wafer may reside in contact with the disk where the wafer pocket is formed into said disk. The pedestal may be rotated about the central longitudinal axis of the shaft to move the disk, susceptor, and wafer axially within the process chamber.
Rotation during processing facilitates an improved and more uniform heat and chemical dissipation upon the wafer disk. However, this process requires the wafer to be concentric with respect to the process chamber as well as parallel with the chamber ceiling, at all rotational angles of the riser shaft. The concentricity and parallelism tolerances are extremely small and critical for the proper application of heat and chemicals within the process chamber. Often a pedestal style heater does not conform to the required tolerances either through manufacturing inadequacies or through normal handling by parties subsequent to the manufacturing, such as inspectors, cleaning houses, and packers. A pedestal style heater which is not within the required tolerances facilitates both lateral runout of the wafer, where the parallelism between the wafer and the chamber ceiling changes while spinning, and radial runout of the wafer, where the wafer is not concentric within the process chamber while spinning. A technician can center the wafer within the chamber and set the wafer parallel to the chamber ceiling before rotation, however, if the pedestal style heater is not within the required tolerances, the wafer will experience lateral and/or radial runout during axial rotation. Thus, there is a tremendous need in the art to compensate for pedestal style heaters which do not conform to required tolerances, particularly with respect to the perpendicularity between the disk and the shaft.